1. Field of the Invention
The present invention relates to a cathode-ray tube apparatus having a cathode-ray tube and a deflection yoke, and more particularly to a cathode-ray tube apparatus and its yoke capable of suppressing a high frequency electric field radiated from the deflection yoke and a deflection and high voltage circuit to the outside of the apparatus.
2. Description of the Related Art
As a first conventional related art, there is known a cathode-ray tube apparatus described in JP-A-61-138433 wherein a non-magnetic conductive shield member of a ring shape covers the focusing electrode system having an electron gun sealed within the neck portion of the cathode-ray tube and magnetic cores of the deflection yoke.
As a second conventional related art, there is known a cathode-ray tube apparatus disclosed in JP-A-62-241242 wherein a saddle-shaped horizontal deflection coil on a deflection yoke core is connected to a cancellation toroidal coil mounted on the yoke core, to generate a magnetic field opposite in polarity to the horizontal deflection magnetic field leaked from the horizontal deflection coil outside of the deflection yoke assembly. This apparatus aims at canceling the leakage magnetic field and is not intended to cancel and reduce an electric field.
A sawtooth waveform current of a horizontal deflection period is required to flow in the horizontal deflection coil on the deflection yoke. A high pulse voltage is therefore applied to the horizontal deflection coil. A high frequency electric field is generated by this pulse voltage and radiated from the deflection yoke to the outside of the apparatus. With a conventional technique, a pulse voltage opposite in polarity to that applied to the horizontal deflection coil is generated, and the electric field of this pulse voltage is radiated to the outside to reduce the high frequency electric field radiated from the deflection yoke to the outside. As a third conventional related art, there is known a cathode-ray tube apparatus described in SID 92' Digest 1992, pp. 135 to 140 wherein in order to cancel and reduce the high frequency electric field radiated outside of the cathode-ray tube apparatus, a coil for generating a pulse voltage opposite in polarity to the pulse voltage applied to the horizontal deflection coil is coupled to the flyback transformer, and the reverse pulse voltage generated by the coil is applied to an electric field radiator for the cancellation and reduction of the high frequency electric field.
In a general cathode-ray tube apparatus, when the horizontal deflection magnetic field is generated by applying a high pulse voltage to the horizontal deflection coil on the deflection yoke, a high frequency electric field is radiated from the deflection yoke and deflection and high voltage circuit to the outside of the cathode-ray tube apparatus. This high frequency electric field may interfere with other electronic apparatuses near the cathode-ray tube apparatus and may be injurious to users. It is therefore necessary for a cathode-ray tube apparatus to reduce a high frequency electric field radiated to the outside.
However, the first conventional related art aims at preventing the locus of an electron beam from not being influenced by the leakage magnetic field changing in time and radiated from the flyback transformer or the like of the deflection and high voltage circuit, and does not consider the reduction of a high frequency electric field radiated from the deflection yoke and deflection high voltage circuit to the outside of the cathode-ray tube apparatus. Furthermore, since the aperture of the horizontal deflection coil applied with a high pulse voltage is not covered with a shielding member, the high frequency electric field radiated from the deflection yoke to the outside of the cathode-ray tube apparatus can be hardly reduced.
The second conventional related art aims at generating a magnetic field which cancels the leakage magnetic field of the deflection yoke by flowing a current in the cancellation coil, and does not consider the reduction of the high frequency electric field radiated from the deflection yoke and deflection and high voltage circuit to the outside of the cathode-ray tube apparatus.
The third conventional related art provides the flyback transformer having the coil for generating an opposite polarity pulse voltage, without considering the deflection yoke itself which is the main source of radiating the high frequency electric field. Lead wires are therefore necessary for the connection from the coil of the flyback transformer to the electric field radiator mounted on the deflection yoke. It is necessary to mount such an electric field radiator so that it covers the inner surface of the horizontal deflection coil to reduce the electric field generated toward the front surface of the cathode-ray tube. In this case, if a plate type conductive material is used for the electric field radiator, an eddy current will be generated by the horizontal deflection magnetic field, posing a problem of heat generation. To solve this problem, it has been necessary to mount the electric field radiator not directly on the deflection yoke but on other sites near the cathode-ray tube apparatus.